The scale of the antimicrobial resistance crisis provides the urgent context for this work. According to figures cited in the review, 1.27 million deaths were attributed to drug-resistant infections in 2019 alone, and projections suggest that deaths associated with AMR could reach 8.22 million annually by 2050. The extensive use of antimicrobial drugs in poultry production, for growth promotion, disease prevention and treatment, has driven the emergence of resistant avian pathogens and multidrug-resistant bacterial strains that threaten both animal health and food safety. Drug residues in poultry meat and eggs compound the problem, while manure containing up to 90 percent of consumed drug doses acts as a conduit for resistance genes into soil and water systems, where they can persist unaltered for many years.

The review frames medicine’s history in three phases: a pre-antibiotic era before 1935, the antibiotic era beginning in 1935, and the post-antibiotic era initiated around 2010. While a few decades of antibiotic use represented a golden age for treating once-fatal infections, the pipeline for new synthetic antimicrobials has essentially run dry. At the same time, resistance mechanisms transfer both vertically and horizontally between microbial populations, and governance strategies for AMR vary considerably between countries. Against this backdrop, the authors argue that the bioactive compounds found in medicinal plants, refined by millennia of traditional use, represent the most viable pathway forward for maintaining poultry productivity without perpetuating the resistance crisis.

Technically, the therapeutic power of medicinal plants rests on an extraordinary chemical arsenal. The review notes that over 300,000 plant species exist, with a recently compiled database cataloguing 9,225 phytochemicals from medicinal plants. Common bioactive constituents include tannins, saponins, flavonoids and alkaloids, which confer antiviral, antimicrobial, antioxidant, antifungal and anti-inflammatory activities. These compounds operate through diverse mechanisms: some disintegrate viral capsids, others disrupt bacterial outer membranes, stimulate macrophage production, activate T-cell-mediated immune responses, or modulate inflammatory pathways. The World Health Organization reports that 80 percent of the global population already relies on traditional medicine for primary healthcare, and the market value of medicinal plant products has surpassed $100 billion annually.

For bacterial diseases, the review identifies the most economically significant poultry pathogens as Salmonella species, Mycoplasma gallisepticum and avian pathogenic Escherichia coli, all of which have developed worrying levels of antibiotic resistance. Several plant-based interventions show genuine promise. Guava (Psidium guajava) extract at 5 percent concentration inhibits the growth of both Salmonella typhimurium and E. coli O157:H7. Phyllanthus niruri at 62.5 percent concentration is bactericidal against M. gallisepticum in vitro, while quercetin from Ephedra Houttuynia powder performs comparably to the antibiotic tiamulin in treating mycoplasmosis. Against E. coli, combinations of essential oils show synergistic effects: thymol and carvacrol disintegrate the bacterial outer membrane, allowing eugenol to penetrate the cytoplasm and inhibit growth. Rosemary, garlic, onion and mint extracts similarly reduce intestinal E. coli populations.

Viral diseases represent perhaps the greatest unmet need in poultry medicine, since no effective drugs exist for treating avian influenza, infectious bronchitis, Newcastle disease or infectious bursal disease. The review documents several botanical approaches with measurable antiviral activity. Green tea (Camellia sinensis) extract at 50 micrograms per milliliter strongly inhibits avian influenza virus replication in vitro, while Forsythia suspensa and Scutellaria baicalensis extracts act synergistically against infectious bronchitis virus, reducing viral copies and increasing antiviral G3BP1 protein levels in tracheas. St. John’s Wort (Hypericum perforatum) extract at 120 milligrams per kilogram of body weight demonstrates antiviral activity against infectious bronchitis both in vitro and in vivo. Combination formulas containing Withania somnifera, Tinospora cordifolia and Ocimum sanctum have proven effective against H9N2 avian influenza and IBDV co-infections.

Coccidiosis, caused by Eimeria parasites, remains the most economically important parasitic disease in intensive poultry production, and drug resistance has severely limited conventional treatment options. Here too, plants offer credible alternatives. Green tea supplementation at 0.4 grams per kilogram of feed serves as a possible replacement for ionophore drugs, while a saponin-rich premixture from Yucca schidigera and Trigonella foenum-graecum performs as efficiently as monensin under experimental Eimeria challenge. Artemisia annua, Bidens pilosa and garlic each target different stages of the Eimeria life cycle, inhibiting cell wall formation, sporozoite invasion and oocyst sporulation. Notably, combinations of multiple medicinal plants consistently outperform single-plant interventions.

Beyond direct antimicrobial effects, the review highlights the immunomodulatory potential of plant compounds as perhaps their most strategically valuable property in the post-antibiotic era. Carvacrol from oregano essential oil is described as the gold standard for improving chicken health. Nigella sativa oil enhances both humoral and cellular immune responses when administered alongside avian influenza vaccination, and turmeric supplementation at 250 milligrams per kilogram modulates the acute phase response following Newcastle disease vaccination. Curcumin at 100 to 200 milligrams per kilogram significantly increases production of interleukin-2 and interferon-gamma in broilers, while nanoprotected rosemary essential oil at 200 milligrams per kilogram elevates IgG and IgM levels. These findings suggest that rather than simply killing pathogens directly, medicinal plants can strengthen the bird’s own innate defences, a strategy that may prove more durable against evolving microbes.

The review also emphasizes environmental and production benefits. Poultry already has the lowest carbon footprint of all meat-producing animals, at 23 to 37 grams of CO2 equivalents per gram of protein compared to 194 for beef, yet the industry still accounts for roughly 8 percent of livestock sector greenhouse gas emissions. Yucca schidigera extract, rich in saponins, reduces ammonia emissions when added to feed or drinking water, addressing one of the largest environmental liabilities of poultry farming. Additionally, plant-based vaccine technology is emerging as a transformative frontier: transgenic plants expressing viral proteins can produce subunit and virus-like particle vaccines against Newcastle disease, avian influenza, infectious bronchitis and infectious bursal disease, with oral delivery through feed and heat-stable seed-based formulations offering particularly attractive commercial prospects.

The authors conclude that medicinal plants represent the best available alternative for poultry production in the post-antibiotic era, but they stress that significant work remains before widespread commercialization. They recommend rigorous pharmacokinetic and bioavailability studies in target tissues, elucidation of mechanisms of action and potential herb-drug interactions, dose-response trials to establish MIC50 and MIC90 levels, systematic safety and toxicity evaluations, residue studies with withdrawal time determinations, and long-term monitoring for microbial resistance to herbal compounds themselves. They also call for integrating well-defined herbal products into veterinary education, creating awareness among farmers and healthcare professionals, and implementing regular surveillance of drug residues in poultry products. As the microbes continue their relentless adaptation, the review suggests that humanity’s oldest pharmacy, the plant kingdom, may hold the keys to sustainable food production in the decades ahead.